The so-called pin tumbler cylinder lock, or Yale lock, was introduced about 1860 and remains in wide use today. The Yale lock consists essentially of a cylindrical plug placed in an outer barrel. The plug is rotated by a key which in turn moves the bolt of the lock by means of a cam. In order to rotate the plug, the key is inserted and raises a plurality of lock pins of varying lengths different distances depending upon the depths of the key cuts to establish a shear line at the outer surface of the plug when the key and pins match. This shear line permits the plug to be rotated within the barrel operating the lock.
A problem which continually besets locksmiths is the loading of the proper lock pins into the cylindrical cavities (typically 5, 6, or 7 in number) in the plug. For a given lock the lock pins come in two basic types, bottom pins and master pins, and each of these come in a variety of lengths to correspond with the lock's key configuration. The exact combination of proper lock pins must be loaded into each of the cavities in the plug in order for the lock to function. This loading operation is usually performed manually through the use of tweezers, and can be both time consuming and error laden. Prior to loading, the lock pins are usually stored in a partitioned tray which separates the pins of various types and lengths. If lock pins are inadvertently stored in the wrong partition then incorrect pin loading can occur. Additionally, the pin loading operation necessarily demands precision, and is therefore sometimes difficult to perform under job site conditions.